1. Field
The presently disclosed subject matter relates to a light emitting device including a semiconductor light emitting element such as a light emitting diode (LED) and a manufacturing method thereof.
2. Description of the Related Art
Conventional examples of the configuration of a light emitting device, including a substrate having an LED chip mounted thereon and a reflector provided separately from the substrate, are as follows.
Japanese Patent Application Laid-Open Publication No. H11-340517 discloses the configuration of a semiconductor light emitting device wherein a ring-shaped reflector is fixed onto a substrate to surround a semiconductor light emitting element, and wherein the reflector and the semiconductor light emitting element are buried with encapsulating resin.
Japanese Patent Application Laid-Open Publication No. 2004-241509 discloses the configuration of an LED light source which includes a printed substrate having a plurality of LED chips mounted thereon and a conductor pattern for connecting the LED chips formed thereon, a reflector plate having reflector holes provided corresponding to the LED chips, which plate is stuck at its underside to the printed substrate via an adhesive layer, and encapsulating resin filling the reflector holes.
Japanese Patent Application Laid-Open Publication No. 2006-245626 discloses a light emitting diode device which is produced by mounting multiple LED elements at predetermined positions on a substrate and performing wire-bonding and then sticking a reflector frame provided with multiple holes corresponding to the mounting positions of the LED elements arranged on the substrate, onto the substrate and injecting light-transmissive resin to fill the holes provided in the reflector frame and dicing along cutting lines into devices.
Where in the manufacturing process of light emitting devices, an adhesive is used to fix a reflector onto a substrate having an LED chip mounted thereon, the amount of applied adhesive needs to be finely managed. For example, if the amount of adhesive is too large, the adhesive will stick out of the footprint of the reflector and may be in contact with a bonding wire. This results in the bonding wire passing through the interface between the adhesive and encapsulating resin, and hence if the difference in thermal expansion coefficient between the adhesive and the encapsulating resin is large, the breaking of the bonding wire may happen due to a thermal shock, or so on, thus damaging reliability. Even if the encapsulating resin and the adhesive are of the same material, the interface will be formed as long as these are formed at different steps. If peeling-off happens at the interface to the resin layer, in addition to the possibility of wire breaking, light may be reflected or scattered at the peeled-off portion, causing a problem in terms of light distribution design.
On the other hand, if the amount of adhesive is not enough, a space will be produced between the substrate and the reflector, so that air is likely to get confined between the reflector and the substrate when injecting resin. Then, the air introduced under the reflector may intrude into the light emitting area to remain as a bubble in the encapsulating resin, which causes the reflection or scattering of light and thus failure in achieving intended light distribution. Further, if a bubble exists in the encapsulating resin, the bubble may become the starting point of a crack when a thermal shock is applied. Further, if the bubble is in contact with a bonding wire, it may cause wire breaking. Yet further, if variation in the amount of applied adhesive occurs, where the encapsulating resin contains a fluorescence substance, the height of the encapsulating resin will be uneven, which causes chromaticity deviation of emission color. Especially, where a planar light source or a linear light source is configured with a plurality of light emitting elements, this causes color unevenness, and hence variation in the amount of applied adhesive has been a factor in worsening the yield.